Populating HashMaps of HashMap of Objects

Question

I have code I am working on, but I am having issues populating the HashMap of HashMaps. The declaration goes as thus;

HashMap<Games, HashMap<Store, Integer>> myMap = new HashMap<Games, HashMap<Store, Integer>>();

Where Game and Store are separate object classes, with only a class variable title.

How do I create instances of the objects in the HashMaps and also populate the two hashmaps. Because I need to tag an Integer to the game in a particular store. Whereas there are different stores and different games in each store.

Thanks in Advance

Edit

Games Class

package gameStore; public class Games { private String title; public Games(String inTitle){ setTitle(inTitle); } private String getTitle() { return title; } private void setTitle(String title) { this.title = title; } }

Stores Class

package gameStore; public class LocalStores { private String nameOfStore; public LocalStores(String inNameOfStore){ setNameOfStore(inNameOfStore); } private void setNameOfStore(String nameOfStore){ this.nameOfStore = nameOfStore; } }

It seems, like you could also use database for storing that info. There is a DB included into JDK -- Java DB. — Lauri
– Lauri, Commented Mar 12, 2012 at 7:51

Maurice Perry · Accepted Answer · 2012-03-12 09:37:36Z

I would do something like this:

void addToMap(Games games, Store store, int value) { HashMap<Store,Integer> m = myMap.get(games); if (m == null) { m = new HashMap<Store,Integer>(); myMap.put(games, m); } m.put(store, value); }

UPDATE:

Since Games and Store are both used as keys to a HashMap, I would recommand that you add the hashCode and equals methods:

Games:

public int hashCode() { return title.hashCode(); } public boolean equals(Object obj) { if (!(obj instanceof Games)) { return false; } Games other = (Games)obj; return title.equals(other.title); }

LocalStores:

public int hashCode() { return nameOfStore.hashCode(); } public boolean equals(Object obj) { if (!(obj instanceof LocalStores)) { return false; } LocalStores other = (LocalStores)obj; return nameOfStore.equals(other.nameOfStore); }

Now, to keep it simple, let's say that each line of your input file contains three fields separated by tabs: the games' title, the store's name, and the integer value. You would read it as follows:

InputStream stream = new FileInputStream("myfile"); try { Reader reader = new InputStreamReader(stream, "UTF-8"); // or another encoding try { BufferedInputStream in = new BufferedInputStream(reader); try { String line = in.readLine(); while (line != null) { String[] fields = line.split("[\\t]"); if (fields.length == 3) { addToMap(new Games(fields[0]), new LocalStores(fields[1]), Integer.parseInt(fields[2])); } line = in.readLine(); } } finally { in.close(); } } finally { reader.close(); } } finally { stream.close(); }

Hello Maurice, can you please explain what you are trying to say?
this code will map an integer to a couple (Games,Store). The integer can then be retrieved by doing myMap.get(games).get(store).
Okay.. But I am thinking of populating the Objects here... To populate the objects with strings from a file... as the title... and then create instances of the objects into the Map before assigning the generated random Integer to assign... then query from within the HashMap. Can you please be descriptive about this...
As someone commented, you didn't provide the code for Games and Store. Difficult to know how to read these things...

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